The diamond miner recovered the stone from the Cullinan Mine in September, and sold it via a tender held at its diamond marketing offices in Johannesburg earlier this month for $14.9 million, or about $741,000 per carat.

Cathy Malins, a Petra spokeswoman, said in the 10 years the company has been operating the mine this is the second highest price per carat achieved for a blue diamond, a “testament to its very high quality.”

The highest was a 29.6-carat blue rough that sold for $25.6 million, or nearly $863,000 per carat. That stone was cut into a 12-carat diamond that sold for $48.5 million in 2015 and was dubbed the “Blue Moon of Josephine.”

Petra said a “leading diamond company” bought the 20.08-carat stone but wishes to remain anonymous.

Petra Chief Executive Richard Duffy said in a press release the result is what the company expected and “confirms the resilience in the value of very high-quality blue diamonds.”

“We look forward to following this exceptional stone’s journey to its polished form.”

Also on Friday, the London-based diamond miner announced it is restructuring in order to better support its operations and speed up implementation of Project 2022, a three-year plan to cut debt.

The mines now report directly to Chief Executive Richard Duffy, and the chief operating officer role has been eliminated.

As a result, current COO Luctor Roode is leaving the company immediately.

Duffy said: “Luctor has been instrumental in leading the operations’ transition to steady state operational performance following a long period of capital investment across our mines and I would like to thank him for his significant contribution to the company over the last eight years.

“He leaves Petra at a time when the Company is delivering solid and consistent production results across the operations and I am certain that he will be successful in his future endeavors. We wish him well.”